/*
 * Copyright (c) 2016-2018 Contributors to the Eclipse Foundation
 *
 * See the NOTICE file(s) distributed with this work for additional
 * information regarding copyright ownership.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * You may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Configuration for Java MicroProfile
 *
 * <h2>Rationale</h2>
 *
 * <p>
 * For many project artifacts (e.g. WAR, EAR) it should be possible to build them only once and then install them at
 * different customers, stages, etc. They need to target those different execution environments without the necessity of
 * any repackaging. In other words: depending on the situation they need different configuration.
 *
 * <p>
 * This is easily achievable by having a set of default configuration values inside the project artifact. But be able to
 * overwrite those default values from external.
 *
 * <h2>How it works</h2>
 *
 * <p>
 * A <em>Configuration</em> consists of the information collected from the registered
 * {@link org.eclipse.microprofile.config.spi.ConfigSource ConfigSources}. These {@code ConfigSources} get sorted
 * according to their <i>ordinal</i>. That way it is possible to overwrite configuration with lower importance from
 * outside.
 *
 * <p>
 * By default there are 3 ConfigSources:
 *
 * <ul>
 * <li>{@code System.getProperties()} (ordinal=400)</li>
 * <li>{@code System.getenv()} (ordinal=300)</li>
 * <li>all {@code META-INF/microprofile-config.properties} files on the ClassPath. (ordinal=100, separately configurable
 * via a config_ordinal property inside each file)</li>
 * </ul>
 *
 * <p>
 * That means that one can put the default configuration in a {@code META-INF/microprofile-config.properties} anywhere
 * on the classpath and the Operations team can later simply e.g set a system property to change this default
 * configuration.
 *
 * <p>
 * It is of course also possible to register own {@link org.eclipse.microprofile.config.spi.ConfigSource ConfigSources}.
 * A {@code ConfigSource} could e.g. read configuration values from a database table, a remote server, etc
 *
 * <h2>Accessing and Using the Configuration</h2>
 *
 * <p>
 * The configuration of an application is represented by an instance of {@link org.eclipse.microprofile.config.Config}.
 * The {@link org.eclipse.microprofile.config.Config} can be accessed via the
 * {@link org.eclipse.microprofile.config.ConfigProvider}.
 *
 * <pre>
 * Config config = ConfigProvider.getConfig();
 * String restUrl = config.getValue("myproject.some.endpoint.url", String.class);
 * </pre>
 *
 * <p>
 * Injection via a JSR-330 DI container is also supported:
 *
 * <pre>
 * &#064;Inject
 * &#064;ConfigProperty(name="myproject.some.endpoint.url");
 * private String restUrl;
 * </pre>
 *
 * @author <a href="emijiang@uk.ibm.com">Emily Jiang</a>
 * @author <a href="mailto:struberg@apache.org">Mark Struberg</a>
 */
@org.osgi.annotation.versioning.Version("3.0.0")
package org.eclipse.microprofile.config;
